In multi-cylinder reciprocating piston devices, such as compressors and engines, it is often desirable to arrange the cylinders in a V relationship, with respect to one another, to provide a device that is more compact than the device would be if the cylinders were arranged in a straight row, or diametrically opposed to one another. As the pistons reciprocate, in any reciprocating piston device, the motion of the pistons in the cylinders, together with the motions and rotations of other parts of the device, such as a crankshaft and connecting rods joining the pistons to the crankshaft, generate unbalance loads that must be counterbalanced for smooth and quiet operation of the device. Arranging the cylinders in a V relationship, can, in some instances, introduce unbalance loads during operation of the engine, which are unique to the number of cylinders and the included angle between the cylinders. Certain combinations of cylinder numbers and included angles are more readily balanced than other combinations, and as a general rule, the more cylinders that the device has, the easier it will be to achieve an acceptably low level of vibration and noise.
In a V-twin reciprocating device, having only two cylinders arranged in a V relationship to one another, the motion of the components creates an inherent unbalance load that has traditionally been difficult to counterbalance, except at certain specific angular relationships between the cylinders, such as 60 or 90 degrees, with both pistons attached to a common journal of the crankshaft. If it is desired to utilize another angular relationship, some form of internal balancing must be provided.
If the V-twin reciprocating apparatus is an engine, there is an additional problem to be addressed. A 90° V-twin engine with a single crank pin for both connecting rods can be balanced, but fires at uneven alternate intervals of 270 and 450 degrees of crankshaft rotation. Similarly, a 60° V-twin engine with a common pin could also be balanced, but would fire at uneven alternate intervals of 300 and 420 degrees of crankshaft rotation. Having the cylinders fire at an uneven interval generates vibration and noise that is objectionable in environments such as an automobile. It is desirable that a V-twin engine fire at even intervals of 360°, to produce a more acceptable vibration and sound profile for an automotive environment.
What is needed is an improved V-twin reciprocating apparatus, and an improved method for operating a V-twin reciprocating device, that facilitate smooth and quiet operation of the V-twin reciprocating apparatus.